Automated digitized system and methods for verifying power relay disconnect

ABSTRACT

Systems and methods for automatically verifying that power relays have been disconnected include relays arranged between two power sources. Test nodes are positioned between the relays on each line, and feed into a detection circuit. Voltage drop resistors, voltage drop diodes, an optocoupler, and additional resistors and capacitors are used to provide voltage isolation for the detection circuit. Relays are methodically opened and closed to check the individual functioning of each relay, and a digital signal generated from the detection circuit. The design of the system with detection circuit isolation provides a safer and lower cost system for verifying that relays are operating correctly, with less costly components than traditional systems.

TECHNICAL FIELD

The present disclosure relates to the field of power sourcetechnologies, and specifically, relates to a circuit and methods forautomatically verifying that power relays have been appropriatelydisconnected.

BACKGROUND OF THE INVENTION

Renewable energy, in particular photovoltaic (PV) solar energy, hasbecome globally widespread. PV energy systems are frequently connectedto an energy storage system (ESS), typically a direct current (DC)battery and inverter, to allow for storage and controlled distributionof energy. The ESS is commonly connected to a nearby alternating current(AC) utility grid and/or a local AC energy load. The ESS is capable ofoperating in at least two modes, including grid-connected (grid-tied) orislanded mode (also named back-up mode or off-grid mode). In addition toor in place of PV solar energy systems, the ESS may be connected toother renewable energy sources such as wind power or hydroelectricpower, or other inverters or standard fuel-power generators.

A power inverter is an electronic device that changes DC to AC, andvice-versa. An inverter is required to effectively use battery powerfrom an ESS in many common applications, because batteries operate on DCand both the utility grid and common electronics operate on AC. Theinput voltage, output voltage, frequency, and overall power handlingdepend on the design of the inverter.

Traditional power inverters utilize transformers and are isolated. Morerecently, non-isolated inverters that do not utilize transformers arebeing used. In order to achieve isolation for these newer inverters,disconnect relays and other methods are used.

Safety is a primary concern when dealing with high voltage systems andhigh capacity energy storage systems. If, for example, there is a poweroutage caused by a downed transmission line, it is critical that energystorage systems be properly disconnected and go off-grid. If the systemis not properly disconnected, electricity may flow back through thetransmission lines and cause a safety concern for the line workers.

The proper functioning of the disconnect means is important to maintain.In high-voltage systems, disconnect relays may inadvertently becomestuck or welded together. In such cases, an ESS may not properly gooff-line in the event of a power outage and may create a safety concern.Therefore, it is important to test the proper functioning of disconnectmeans.

In order to ensure safety in traditional systems, analog sensing is usedto ensure that the disconnect means are functioning properly. The linesare simply tested to determine if there is current running through them.However, there are several disadvantages of analog sensing systems usedto ensure relays are disconnected properly, including but not limited tothe fact that they are usually not isolated from the high-voltage lines,an additional voltage reference is needed to offset the negative voltagereading when used with an AC source, an additional isolated power supplyis required to use isolated analog sensing, and additional parts makethe analog sensing system more expensive and complex. The fact that mostcommonly used analog sensing systems are not isolated presents safetyconcerns in and of itself, as high-voltage current may be runningthrough easily-accessible areas of the inverter or other equipment.

Therefore, in order to ensure safety and prevent unintentional contact(shorts), it is desirable to have an isolated, automatic means ofverifying that the power relays are disconnected. The digital detectioncircuit and methods herein provide a system that is effectivelyisolated, trustworthy, less parts-intensive, and more cost effectivethat prior systems and methods. Since the signals are digital here, onecan use these signals to perform additional logic as required withoutneeding a microprocessor or controller. The present invention thereforeenjoys the benefits of being safer and less expensive than conventionalsystems for verifying disconnect of power relays.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide an automated,digitized system and methods to test and ensure the proper functioningof disconnect means, including but not limited to relays. It is afurther object of the present invention to provide a system and methodsto test disconnect means that is both safer and more cost-effective thanexisting systems and methods.

In one embodiment of the present invention, a detection circuit isprovided for a single-phase or bi-phase power system. A disconnectcircuit is provided between two active voltage sources. The two voltagesources are connected by two legs, with each leg containing two relaysin series as required by safety compliance. A detection circuit isconnected between the two relays on each leg. The detection circuit maybe composed of voltage drop resistors, voltage drop diodes, anoptocoupler, and other pull-down and pull-up resistors and filtercapacitors, as will be understood by one of ordinary skill in the art.The relays may be controlled by a microprocessor or similar device, andmay be achieved by manual switch and analog and/or digital signals. Thedetection circuit will be activated when the relays are configured toallow current to flow through the detection circuit. Utilizing themethods described herein, each relay can be individually tested toensure proper functioning of the disconnect circuit.

In another embodiment, a detection circuit is provided for a three-phaseor multi-system. Three or more legs, as needed, are provided with tworelays each in series. A detection circuit is provided between therelays of each leg, as above. Utilizing the methods described herein,each relay can be individually tested to ensure proper functioning ofthe disconnect circuit.

The present invention may be used in electronic equipment including butnot limited to inverters and converters, and in connection withapplications including but not limited to battery chargers, capacitorbanks for connecting active power sources, PV inverters and motordrives, as understood by one of ordinary skill in the art. The presentinvention may be adapted to single-phase applications or multi-phaseapplications, including but not limited to three-phase applications. Byutilizing the teachings of the present invention, a safe and effectivetest of the disconnect means can be achieved at relatively low cost andwith minimal parts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic showing the lines and relays of a single-phase andbi-phase application of the present invention.

FIG. 2 is a schematic showing the detection circuit of a single-phaseand bi-phase application of the present invention.

FIG. 3 is a schematic showing the lines and relays of a three-phase andmulti-phase application of the present invention.

FIG. 4 is a schematic showing the detection circuit of a three-phase andmulti-phase application of the present invention.

FIG. 5 is a Table showing various test conditions for the relays of asingle-phase and bi-phase application of the present invention.

FIG. 6 is a schematic showing the lines and relays of a typical priorart system.

FIG. 7 is a schematic showing the voltage sensing apparatus on a firstpower source side of a typical prior art system.

FIG. 8 is a schematic showing the voltage sensing apparatus on a secondpower source side of a typical prior art system.

FIG. 9 is a schematic showing the voltage sensing apparatus between therelays of a typical prior art system.

DETAILED DESCRITION OF THE INVENTION

The invention relates generally to an energy storage system utilizing anon-isolated inverter. In order to ensure safety and preventunintentional contacts (shorts), it is essential to confirm properfunctioning and disconnection of power relays. A low-cost isolateddigital system is provided for automatically verifying that power relayshave been disconnected.

FIG. 1 depicts the line and relay configuration of one embodiment of thepresent invention. A first voltage source 100 and a second voltagesource 101 are provided, and are connected by a first line 102 and asecond line 103. One of ordinary skill in the art will understand thatthe first and second voltage sources could be any AC or DC power source,including but not limited to a power inverter or the electrical utilitygrid.

Relays 105, 106, 107, and 108 are positioned on the lines as shown inFIG. 1 . In between relays 105 and 106 is a line-one relay test node111, which connects into the test circuit depicted in FIG. 2 . Inbetween relays 107 and 108 is a line-two relay test node 112, which alsoconnects into the test circuit depicted in FIG. 2 .

The relays are generally composed of contact terminals and coils,although other configurations known to one of ordinary skill in the artmay be used. The relay contact is connected in series with the line ofthe voltage sources, and a coil is used to drive the relay contact. Eachrelay is driven by a driver, which could be transistor. One end of thecoil is connected to a low voltage source, for example voltage source121. The transistor connects the other end of the relay coil to theground (for example, ground 122) when activated. By using an appropriatetransistor, the transistor can be used to connect the (+)ve or (—)ve endof low voltage source to a relay terminal. A diode is used to suppressreverse potential generated on the relay coil and protect the transistorwhen the relay is turned from an on (closed) state to an off (open)state. Turning the relay from an off to on state may be achieved bymeans of a microprocessor or similar device, as well as by manual switchor analog and digital signals.

A detection circuit of one embodiment of the present invention is shownin FIG. 2 . The detection circuit is composed mainly of voltage dropresistors, voltage drop diodes, an optocoupler and other pull-down andpull-up resistors along with filter capacitors. This results in voltageisolation of the detection circuit. However, other configurations may beused as understood by one of ordinary skill in the art. If isolation isnot desired, then the detection circuit can be replaced with voltagelevel converting circuits like resistive divider networks.

The detection circuit in FIG. 2 is coupled to the relays by virtue oflines running from nodes 111 and 112 in FIG. 1 . The output of thedetection circuit is obtained from detector node 125, which is isolatedas a result of the series of voltage drops between nodes 111 and 112 andoptocoupler 124. Optocoupler 124 assists in making the test circuitdetermination. When current is flowing through both nodes 111 and 112(from either or both of the voltage sources), there is a closed circuitrunning through optocoupler 124. This drives the optocoupler transistorand makes the impedence low at every peak of the AC cycle and highimpedance for non-peak AC cycles, which makes the output signal from thedetector voltage source 121 low for every peak of the AC cycle and highfor non-peak AC cycles. This produces a corresponding output signalvalue of “0” for every peak AC cycle and “1” for non-peak AC cycles atthe detector node 125, and demonstrates that the test circuit itself isworking and that a pair of relays is able to close properly. If currentis flowing through only node 111 or node 112, but not both, then thereis not a closed circuit running through optocoupler 124. The impedanceis therefore high, causing a high detector voltage to flow from source121 through the detector node 125. In this circumstance, there is anoutput value of “1” from the detector node 125. This may be used toverify that a relay or group of relays is opened properly. One or bothvoltage sources may be engaged in any given test condition.

FIG. 5 presents Table 1, which shows the test conditions for the variousrelays 105, 106, 107, and 108 in the single-phase and bi-phaseapplications of FIG. 1 . The first column shows that in this embodimentthere are three general steps in a method for operating the testcircuit. In the first step, two tests are performed. First, in Case 1, asignal is sent to turn off and open relays 106 and 108 and to turn onand close relays 105 and 107. This allows current to flow through relays105 and 107 and, consequently, nodes 111 and 112. This activates theoptocoupler 124, resulting in a “0” for every peak of the AC cycle and“1” for non-peak AC cycles at detector node 125. Second, in Case 2, thereverse is performed with 106 and 108 on and 105 and 107 off. These twotests tentatively verify that the detection circuit is working and thatthe relays are not stuck open.

In Step 2, three tests are performed to verify that relays 105 and 106are opening properly and are not stuck closed. In Case 3, only voltagesource 101 is used. Relay 107 is set to on, or closed, and relay 105 isset to off, or open. If relay 105 is opening (disconnecting) correctly,the test circuit receives current only from node 112, but not node 111.The optocoupler is therefore in an off position, allowing current toflow from source 121 to detector node 125, and resulting in an outputsignal of “1”. This verifies that relay 105 is properly open. In Case 4,a similar test is performed on relay 106 using voltage source 100 and byturning relay 106 off and relay 108 on. Then, in Case 5, both relays 105and 106 are tested simultaneously to verify that both are opening anddisconnecting properly. Step 3, Cases 6-8, follow the same generalpattern as step 2 and are used to test relays 107 and 108.

One of ordinary skill in the art will understand that the steps outlinedabove are a logical, systematic method of checking each of thedisconnect relays in the embodiment shown in FIG. 1 . However, there area variety of permutations of cases that could be used to test thedisconnect relays, and the order of testing can be rearranged.Therefore, Table 1 in FIG. 5 is provided as an example only, and is notintended to limit the invention.

FIGS. 3 and 4 expand on the single-phase and bi-phase applications ofFIGS. 1 and 2 , and provide line and relay configurations and testcircuits for three-phase and multi-phase applications in anotherembodiment of the present invention. From FIGS. 3 and 4 , and utilizingthe principles in Table 1 of FIG. 5 which gives step by step operationsfor the single-phase and bi-phase applications, one of ordinary skill inthe art will understand how to operate the line relays and test circuitconditions in order to ensure functioning of the disconnect means in athree-phase or multi-phase application.

FIGS. 6-9 show prior art methods of disconnecting two voltage sources,and typical means of testing the disconnection. In FIG. 6 , two activesources are provided as in FIG. 1 . However, as can be seen by thedesign of the test circuits in FIGS. 7-9 , six nodes are required inFIG. 6 to test the relays as opposed to just two in FIG. 1 . The analogdetection circuits presented in in this prior art example utilize Opampsensing or similar analog sensing technology and resistors. Additionalvoltage references are required to offset the reading for negativevoltage when AC sources are used. A DSP, microprocessor, or similardevice is required to compute voltage levels and perform logicaloperation. Overall, this design uses more parts and is more expensivethan the embodiments of the present invention. Moreover, theconfiguration and detection circuits shown in 6-9 are not isolated, andtherefore present safety concerns when accessing the circuits.

One of ordinary skill in the art will understand how to implement theembodiments of the present inventions in these applications to achievethe benefits of a low cost digital system for automatically verifyingthat the power relays have been disconnected. The invention may be usedin any electronics application where a relay, contactor, manual circuitbreaker, manual switch or derivative such as a solid-state relay, powerrelay, electronic relay, or similar device is used as the disconnectmeans.

The above-described embodiments of the present invention are intended tobe examples only. Alterations, modifications, and variations may beeffected to the particular embodiments by those of skill in the artwithout departing from the scope of the invention, which is definedsolely by the claims appended hereto.

What is claimed is:
 1. A method for testing whether power relays areoperable, comprising the steps of: providing two lines arranged inparallel between two voltage sources to allow for bi-directional currentflow between the two voltage sources; providing two relays connected inseries on each line; providing a test line arranged between the tworelays on each line; providing a test circuit directly connected to thetest lines; closing each relay individually in series, while setting theremaining relays to remain open; operating the voltage source nearest tothe closed relay; observing the output of the test circuit; generating areport that indicates whether each relay is operable; closing the relaysthat are nearest to a given voltage source, while setting the relaysnearest the other voltage source to remain open; and operating bothvoltage sources.
 2. The method of claim 1, further comprising the stepsof: opening the relays on a single line, while setting the relays on theremaining lines to remain closed; and operating both voltage sources.